Stent Mandrel Fixture And Method For Reducing Coating Defects

ABSTRACT

A stent mandrel fixture for supporting a stent during the application of a coating substance is provided.

This application is a divisional application of U.S. application Ser.No. 10/255,913, filed Sep. 26, 2002, which is incorporated herein byreference in its entirety.

TECHNICAL FIELD

This invention relates generally to stent mandrel fixtures, and moreparticularly, but not exclusively, provides a stent mandrel fixture andmethod for reducing coating defects on stents.

BACKGROUND

Blood vessel occlusions are commonly treated by mechanically enhancingblood flow in the affected vessels, such as by employing a stent. Stentsact as scaffoldings, functioning to physically hold open and, ifdesired, to expand the wall of affected vessels. Typically stents arecapable of being compressed, so that they can be inserted through smalllumens via catheters, and then expanded to a larger diameter once theyare at the desired location. Examples in the patent literaturedisclosing stents include U.S. Pat. No. 4,733,665 issued to Palmaz, U.S.Pat. No. 4,800,882 issued to Gianturco, and U.S. Pat. No. 4,886,062issued to Wiktor.

FIG. 1 illustrates a conventional stent 10 formed from a plurality ofstruts 12. The plurality of struts 12 are radially expandable andinterconnected by connecting elements 14 that are disposed betweenadjacent struts 12, leaving lateral openings or gaps 16 between adjacentstruts 12. Struts 12 and connecting elements 14 define a tubular stentbody having an outer, tissue-contacting surface and an inner surface.

Stents are used not only for mechanical intervention but also asvehicles for providing biological therapy. Biological therapy can beachieved by medicating the stents. Medicated stents provide for thelocal administration of a therapeutic substance at the diseased site.Local delivery of a therapeutic substance is a preferred method oftreatment because the substance is concentrated at a specific site andthus smaller total levels of medication can be administered incomparison to systemic dosages that often produce adverse or even toxicside effects for the patient.

One method of medicating a stent involves the use of a polymeric carriercoated onto the surface of the stent. A composition including a solvent,a polymer dissolved in the solvent, and a therapeutic substancedispersed in the blend is applied to the stent by immersing the stent inthe composition or by spraying the composition onto the stent. Thesolvent is allowed to evaporate, leaving on the stent strut surfaces acoating of the polymer and the therapeutic substance impregnated in thepolymer.

A shortcoming of the above-described method of medicating a stent is thepotential for coating defects. While some coating defects can beminimized by adjusting the coating parameters, other defects occur dueto the nature of the interface between the stent and the apparatus onwhich the stent is supported during the coating process. A high degreeof surface contact between the stent and the supporting apparatus canprovide regions in which the liquid composition can flow, wick, andcollect as the composition is applied. As the solvent evaporates, theexcess composition hardens to form excess coating at and around thecontact points between the stent and the supporting apparatus. Upon theremoval of the coated stent from the supporting apparatus, the excesscoating may stick to the apparatus, thereby removing some of the coatingfrom the stent and leaving bare areas. Alternatively, the excess coatingmay stick to the stent, thereby leaving excess coating as clumps orpools on the struts or webbing between the struts.

Accordingly, a new stent mandrel fixture is needed to minimize coatingdefects.

SUMMARY

In accordance with one embodiment, a stent mandrel fixture forsupporting a stent during application of a coating substance to thestent is provided, comprising: a first member for supporting a first endof the stent, at least a portion of the first member being made from orbeing coated with a non-stick material for preventing the coatingsubstance from adhering to the first member; a second member forsupporting a second end of the stent, at least a portion of the secondmember being made from or being coated with the non-stick material; anda third member connecting the first member to the second member andextending through a longitudinal bore of the stent. The first or secondmember can have a domed shaped end, a flat end or can have grooves forreceiving the coating substance. Examples of the non-stick materialinclude poly (tetrafluor ethylene), fluorinated ethylene propylene, poly(vinylidene fluoride), poly (para-xylyene), and polyolefin.

In accordance with another embodiment of the invention, a stent mandrelfixture for supporting a stent during application of a coating substanceto the stent is provided, comprising: a first member for contacting afirst end of the stent, the first member having a domed shaped end; asecond member for contacting a second end of the stent, the secondmember having a domed shaped end; and a third member connecting thefirst member to the second member and extending through a longitudinalbore of the stent, wherein the stent can be securely pinched between thedomed shaped ends of the first and second members.

In accordance with yet another embodiment of the invention, a stentmandrel fixture for supporting a stent during application of a coatingsubstance to the stent is provided, comprising: a first member forcontacting a first end of the stent, the first member having a flat end;a second member for contacting a second end of the stent, the secondmember having a flat end; and a third member connecting the first memberto the second member and extending through a longitudinal bore of thestent, wherein the stent can be securely pinched between the flat endsof the first and second members.

In accordance with another embodiment of the invention, a stent mandrelfixture for supporting a stent during application of a coating substanceto the stent is provided, comprising: a first member for contacting afirst end of the stent, the first member having grooves for receivingthe coating substance; a second member for contacting a second end ofthe stent, the second member having grooves for receiving the coatingsubstance; and a third member connecting the first member to the secondmember and extending through a longitudinal bore of the stent, whereinthe stent can be securely pinched between the ends of the first andsecond members. In one embodiment, the first or second member is conedshape and the grooves extend longitudinally across the cone. In anotherembodiment, the grooves extend around the perimeter of the cone.

In accordance with another aspect of the invention, methods of coating astent using the above-described fixtures are provided.

BRIEF DESCRIPTION OF THE DRAWINGS

Non-limiting and non-exhaustive embodiments of the present invention aredescribed with reference to the following figures, wherein likereference numerals refer to like parts throughout the various viewsunless otherwise specified.

FIG. 1 illustrates a conventional stent;

FIG. 2 illustrates a stent mandrel fixture in accordance with anembodiment of the invention;

FIG. 3 illustrates an expanded view of stent mandrel fixture of FIG. 2;

FIG. 4 illustrates a cross section of a second embodiment of a stentmandrel fixture;

FIG. 5 illustrates a cross section of a third embodiment of a stentmandrel fixture;

FIG. 6 illustrates a cross section of a fourth embodiment of a stentmandrel fixture; and

FIG. 7A illustrates a cross section of a fifth embodiment of a stentmandrel fixture;

FIG. 7B illustrates a perspective view of the fifth embodiment of thestent mandrel fixture; and

FIG. 8 illustrates a perspective view of a sixth embodiment of a stentmandrel fixture.

DETAILED DESCRIPTION

The following description is provided to enable any person havingordinary skill in the art to make and use the invention, and is providedin the context of a particular application and its requirements. Variousmodifications to the embodiments will be readily apparent to thoseskilled in the art, and the generic principles defined herein may beapplied to other embodiments and applications without departing from thespirit and scope of the invention. Thus, the present invention is notintended to be limited to the embodiments shown, but is to be accordedthe widest scope consistent with the principles, features and teachingsdisclosed herein.

FIG. 2 illustrates a stent mandrel fixture 20 in accordance with anembodiment of the invention. Fixture 20 for supporting stent 10 isillustrated to include a support member 22, a mandrel 24, and a lockmember 26. Support member 22 can connect to a motor 30A so as to providerotational motion about the longitudinal axis of stent 10, as depictedby arrow 32, during a coating process. Another motor 30B can also beprovided for moving support member 22 in a linear direction, back andforth, along a rail 34.

FIG. 3 illustrates an expanded view of stent mandrel fixture 20. Supportmember 22 includes a coning end portion 36, tapering inwardly at anangle φ₁ of about 15° to about 75°, more narrowly from about 30° toabout 60°. By way of example, angle φ₁ can be about 45°. In accordancewith one embodiment of the invention, mandrel 24 can be permanentlyaffixed to coning end portion 36. Alternatively, support member 22 caninclude a bore 38 for receiving a first end 40 of mandrel 24. First end40 of mandrel 24 can be threaded to screw into bore 38 or,alternatively, can be retained within bore 38 by a friction fit. Bore 38should be deep enough so as to allow mandrel 24 to securely mate withsupport member 22. The depth of bore 38 can also be over-extended so asto allow a significant length of mandrel 24 to penetrate or screw intobore 38. Bore 38 can also extend completely through support member 22.This would allow the length of mandrel 24 to be adjusted to accommodatestents of various sizes.

The outer diameter of mandrel 24 can be smaller than the inner diameterof stent 10 so as to prevent the outer surface of mandrel 24 from makingcontact with the inner surface of stent 10. A sufficient clearancebetween the outer surface of mandrel 24 and the inner surface of stent10 should be provided to prevent mandrel 24 from obstructing the patternof the stent body during the coating process. By way of example, theouter diameter of mandrel 24 can be from about 0.010 inches (0.254 mm)to about 0.017 inches (0.432 mm) when stent 10 has an inner diameter ofbetween about 0.025 inches (0.635 mm) and about 0.035 inches (0.889 mm).

Lock member 26 includes a coning end portion 42 having an inwardlytapered angle φ₂. Angle φ₂ can be the same as or different than theabove-described angle φ₁. A second end 44 of mandrel 24 can bepermanently affixed to lock member 26 if end 40 is disengagable fromsupport member 22. Alternatively, in accordance with another embodiment,mandrel 24 can have a threaded second end 44 for screwing into a bore 46of lock member 26. Bore 46 can be of any suitable depth that would allowlock member 26 to be incrementally moved closer to support member 22.Bore 46 can also extend completely through lock member 26. Accordingly,stents 10 of any length can be securely pinched between support and lockmembers 22 and 26. In accordance with yet another embodiment, anon-threaded second end 44 and bore 46 combination is employed such thatsecond end 44 can be press-fitted or friction-fitted within bore 46 toprevent movement of stent 10 on stent mandrel fixture 20.

In order to reduce coating defects, ends 36 and 42 may be coated withone or more polymeric materials having less adhesive force with thecoating substance than with members 22 and 26. Examples of a suitablepolymeric materials include poly (tetrafluor ethylene) (e.g., Teflon®),fluorinated ethylene propylene (“FEP”), poly (vinylidene fluoride)(“PVDF”), poly (para-xylyene), polyamide (Nylon), polyolefins (e.g.,high density poly (ethylene) and poly (propylene)), and polyacetal(Delrin®). In an alternative embodiment of the invention, members 22 and26 may be made of one or more of the non-stick polymeric materials.

FIG. 4 illustrates a cross section of a second embodiment of a stentmandrel fixture 400. Fixture 400 includes a support member 410, amandrel 420, and a lock member 430. Support member 410 and lock member430 each have symmetrical ends 440 having surfaces 450 a and 450 bhaving a radius of curvature to minimize coating defects by minimizingcontact between fixture 400 and stent 10. Curved surfaces 450 a and 450b are in essence domed cylindrical protrusions instead of the conicalshaped configuration of FIG. 2 and FIG. 3. Curved surface 450 a engagesone end of stent 10 and curved surface 450 b engages the other end ofstent 10 so that stent 10 is securely pinched there between. Thediameter of curved surfaces 450 a and 450 b is greater than the outerdiameter of stent 10 as positioned between support member 410 and lockmember 430.

FIG. 5 illustrates a cross section of a third embodiment of a stentmandrel fixture 500. Fixture 500 includes a support member 510, amandrel 520, and a lock member 530. Support member 510 and lock member530 each have symmetrical ends 540 having surfaces 550 a and 550 b thathave small surface changes. While surfaces 550 a and 550 b only show asingle step, other embodiments of the invention may include surfaceseach having a plurality of steps. The unevenness of surfaces 550 a and550 b help minimize the formation of coating defects. Surface 550 aengages one end of stent 10 and surface 550 b engages the other end ofstent 10 so that stent 10 is securely pinched there between. The area ofsurfaces 550 a and 550 b is greater than the outer diameter of stent 10positioned between support member 510 and lock member 530.

FIG. 6 illustrates a cross section of a fourth embodiment of a stentmandrel fixture 600. Fixture 600 includes a support member 610, amandrel 620, and a lock member 630. Support member 610 and lock member630 each have symmetrical ends 640 having substantially flat surfaces650 a and 650 b to minimize coating defects. Surface 650 a engages oneend of stent 10 and surface 650 b engages the other end of stent 10 sothat stent 10 is securely pinched there between. The area of surfaces650 a and 650 b can be greater than the outer diameter of stent 10positioned between support member 610 and lock member 630.

FIG. 7A illustrates a cross section of a fifth embodiment of a stentmandrel fixture 700. Fixture 700 includes a support member 710, amandrel 720, and a lock member 730. Support member 710 and lock member730 each have symmetrical coned ends 740 having groove designs orchannels 750 to minimize coating defects. FIG. 7B illustrates aperspective of a portion of stent mandrel fixture 700. Coned end 740 hasgrooves or channels 750 circumscribing coned end 740. These grooves orchannels 750 enable the flow of composition off coned ends 740 and aredeep enough to receive excess composition applied during the coatingprocess.

FIG. 8 illustrates a perspective view of a sixth embodiment of a stentmandrel fixture. Each end 840 has a grooved design to prevent coatingdefects from forming at the interface between stent 10 and end 840.Coned ends 840 have grooves or channels extending longitudinally from adistal end of coned end 840 to the proximal end of coned end 840. Anysuitable number of channels 850 can be provided around the circumferenceof coned end 840. Grooves or channels 850 enable the composition to becollected in channels 850. Composition can flow off of coned ends 840,thereby minimizing coating defects.

The foregoing description of the preferred embodiments of the presentinvention is by way of example only, and other variations andmodifications of the above-described embodiments and methods arepossible in light of the foregoing teaching. For example, stent mandrelfixtures 400, 500, 600 and 700 may also be coated with a non-stickpolymeric material having less adhesive force with the coating substancethan with the members.

1-17. (canceled)
 18. A method of coating a stent with a substance,comprising: mounting a stent on a stent mandrel fixture, the stentincluding a first and second end and the mandrel including a firstmember, second member and third member, the mounting step including thesteps of placing the first end on the first member including placing thefirst end proximal to a groove disposed on a surface of the firstmember, disposing the third member within the bore of the stent, andplacing the second end on the second member; and applying the substanceto the stent.
 19. The method of claim 18, wherein the mounting stepincludes placing the first and second ends of the stent on a non-stickcoating disposed on at least one of the respective first and secondmembers.
 20. The method of claim 18, wherein the disposing the thirdmember step occurs before the placing the second end step.
 21. Themethod of claim 20, the mounting step further including the step ofconnecting the second member to the third member after the placing thefirst end on the first member step.
 22. The method of claim 21, themounting step further including the step of displacing the second memberrelative to the first member after connecting the second member to thethird member.
 23. The method of claim 21, the mounting step furtherincluding the step of pinching the stent between the first member andthe second member including the step of displacing one of the first andsecond members relative to the other.
 24. The method of claim 23,wherein the pinching step further includes the step of displacing thesecond member over a threading formed on the third member.
 25. Themethod of claim 23, wherein the pinching step further includes the stepof pinching the stent between opposed surfaces, each of the surfacesbeing disposed proximal to a first and second groove formed on therespective first and second members and distal from an end of therespective first second members.
 26. The method of claim 18, wherein theplacing step includes placing the first end against a surface of thefirst member, wherein the surface is proximal to the groove and distalof an end of the first member.
 27. The method of claim 26, wherein theplacing step includes placing the first end against a surface of thefirst member such that no single, continuous groove extends from alocation within the stent bore to a location outside of the stent bore.28. The method of claim 26, wherein the placing step includes placingthe first end against a surface adjacent a groove that circumscribes thebore axis.
 29. The method of claim 27, wherein the placing step includesplacing the first end against a surface such that the groovecircumscribes the bore axis.
 30. The method of claim 29, wherein theplacing step includes placing the first end against a surface such thatthe groove is disposed entirely within the bore of the stent.
 31. Themethod of claim 29, wherein the placing step includes placing the firstend against a surface such that the groove is disposed entirely outsideof the bore of the stent.
 32. The method of claim 26, wherein theplacing step includes placing the first end against a surface of thefirst member such that a first groove is disposed entirely outside thebore of the stent and a second groove is disposed entirely inside thebore of the stent.
 33. The method of claim 32, wherein the placing stepincludes placing the first end against a surface such that the grooveextends continuously from a location within the stent bore to a locationoutside of the stent bore.
 34. The method of claim 33, wherein theplacing step includes placing the first end against a plurality ofsurfaces, each of the surfaces being disposed between grooves.
 35. Themethod of claim 34, wherein the plurality of surfaces surround a boreaxis of the stent.
 36. The method of claim 32, wherein the grooves arechannels having walls, wherein the walls of a channel are orientated atright angles to each other.